## order_books
### Instructions
Build a module named `library` which contains two sub-modules:
- `writers` : which contains:
- `Writer` : a structure with:
- `first_name` : `String`
- `last_name` : `String`
- `books` : `Vec<Book>`
- `books` : which contains:
- `Book` : a structure with:
- `title` : `String`
- `year` : `u64` as its year of publication
A function `order_books` should be created (outside of the previous modules which receives a `Writer` , and orders the set of books alphabetically.
### Expected Functions and Structs
> You'll need to complete the function and structs, and add them to the appropriate place, so that the `main` in the usage can be successfully compiled and run.
```rs
pub struct Writer {
}
```
```rs
pub struct Book {
}
```
```rs
pub fn order_books(writer: & mut Writer) {
}
```
### Example
Here is a program to test your function and structs:
```rs
pub use library::writers::Writer;
pub use library::books::Book;
fn main() {
let mut writer_a = Writer {
first_name: "William".to_string(),
last_name: "Shakespeare".to_string(),
books: vec![
Book {
title: "Hamlet".to_string(),
year: 1600,
},
Book {
title: "Othelo".to_string(),
year: 1603,
},
Book {
title: "Romeo and Juliet".to_string(),
year: 1593,
},
Book {
title: "MacBeth".to_string(),
year: 1605,
},
],
};
println!("Before ordering");
for b in & writer_a.books {
println!("{:?}", b.title);
}
order_books(& mut writer_a);
println!("\nAfter ordering");
for b in writer_a.books {
println!("{:?}", b.title);
}
}
```
And its output:
```sh
$ cargo run
Before ordering
"Hamlet"
"Othelo"
"Romeo and Juliet"
"MacBeth"
After ordering
"Hamlet"
"MacBeth"
"Othelo"
"Romeo and Juliet"
$
```
